The reverberation chambers, or mode-stirred chambers, have in recent years become effective tools in testing e.g. Over-the-Air performance of various wireless communication devices. Such chambers provide a straightforward solution to testing of devices that rely on multipath signal propagation for communication, often known as MIMO (Multiple Input Multiple Output) technologies, and for devices that simultaneously operate using several frequency bands, etc.
The U.S. Pat. Nos. 7,444,264 and 7,286,961, by the same applicant, discloses such reverberation chambers useable to measure e.g. the radiation efficiency of antennas and the total radiated power (TRP) of mobile and wireless terminals such as cellular phones. The same measurement setups that are described in U.S. Pat. Nos. 7,444,264 and 7,286,961 were also used to determine the performance of antenna diversity. Such reverberation chambers can be used to measure transmitting performance in a fading multipath environment, and/or to measure the receive performance by a Bit-Error-Rate (BER) or a Frame-Error-Rate (FER), depending on which system the terminals are designed for.
The reverberation chamber can by making use of the above previous inventions be used for characterizing the complete performance of mobile and wireless terminals, both on transmit and receive, including transmit and receive performance of antennas, amplifiers, signal processing algorithms, and coding. This has opened up a large potential for RF testing in connection with terminals for more advanced mobile communication systems referred to as 3G and 4G (third and fourth generation of mobile communication systems, also called LTE). Such systems make use of more than one antenna for both transmission and reception and will use these to adapt to the fading multipath environment, in order to improve battery life time and data rate. Such systems are known under terms as diversity antenna systems and MIMO (Multiple Input Multiple Output) antenna systems. In order to develop optimum diversity and MIMO systems it will be more important than ever to quantify the performance of the terminals and base station simulators in multipath environments. The reverberation chamber can provide this testing opportunity.
The ultimate testing opportunity of the reverberation chamber is to measure data throughput of the whole communication system with diversity and MIMO capability, from the data input at the base station to the data output at the terminal, or vice versa. This contains the effects of radiated power, the wireless channel and receiver sensitivity in one performance value, referred to as the throughput, being the most important for the user. This throughput is a resulting data transfer rate, and the measurement setup in reverberation chamber is already described in scientific paper (J. Åsberg, A. Skåarbratt, and C. Orlenius, “Over-the-air performance testing of wire-less terminals by data throughput measurements in reverberation chamber”, European Conference on Antennas and Propagation ICAP 2011, 11-15 Apr. 2011, Rome).
The reverberation chamber can always be improved with respect to both measurement accuracy and resemblance to practical environments. The uncertainty is at present good enough compared to alternative measurement techniques, but a more accurate chamber will allow measurements at a lower frequency or in a smaller chamber and at shorter time, which is attractive. The reverberation chamber represents an isotropic multipath environment with a uniform distribution of angles of arrival of the incoming waves over the complete surrounding space. This is a good reference environment for antennas and wireless terminals in multipath with fading.
However, we are part of a rapidly changing world with technological advancements being made in all fields of technology every year. Particularly in the field of wireless technology and telecommunications where there is a new generation of mobile standards approaching, namely the fifth generation (5G), where new problems and technological challenges await. In more detail, in the next generation of mobile standards, devices will possibly be required to be able to both communicate at current frequency ranges 450 MHz-6 GHz and also at higher frequencies, in the range of, 6-100 GHz, which consequently will present new challenges in regards to testing of higher frequencies since the propagation properties of a wireless link is different at the higher frequencies, with less pronounced multipath.
Thus, despite the improvements in measurement accuracy obtained by means of the reverberation chamber in recent years, there is still a need for improvements to support testing of certain devices, and e.g. devices operating under the expected coming generations of mobile standards.